The present invention relates to multiprocessor systems.
The design purpose of a multiprocessor system is generally to increase system throughput, but in some cases it is aimed at reducing a job's turnaround time. If a job has independent tasks, the turnaround time of the job can be reduced by performing parallel processing on the whole or part of the job. In some types of parallel processing, there is a special kind of data that must be synchronized between tasks or shared by more than one processor. Such data must be used exclusively by one processor. For such purposes, a lock word is stored in a main memory. When a processor attempts to access the exclusive data, it sets the lock word if it is not set so as to obtain the right to access. Any of the other processors accessing the exclusive data examine the status of the lock word, and if it has been already set, the processor is denied access to that data until the lock word is reset. Since the lock word is stored in the main memory, there is an inherent delay in the transfer of data, thus placing a limit for the highest speed with which data can be transferred between processors. In addition to this, a dead lock condition can occur when a processor fails to reset the lock word.